Relationship between prolactin responses to ECT and dopaminergic and serotonergic responsivity in depressed patients

The prolactin (PRL) increases in plasma, induced by the electrical stimulus during electroconvulsive therapy (ECT), is a consistent finding that can be studied in order to obtain information about its actions on the brain neurotransmitter systems, the most probable candidates being the serotonergic and the dopaminergic system. Central serotonergic and dopaminergic responsivity may also be assessed using neuroendocrine challenge tests. In this study, we measured the PRL responses during the first ECT of a therapeutic course in 15 male depressive patients, of mean age 49.2 +/- 14.5 (range 22 to 68 years), and score in the HDRS of 29 +/- 8 (range 18 to 43 points). Before the ECT course, we assessed the central serotonergic and dopaminergic responsivities, by measuring the PRL responses to the administration of the serotonin uptake inhibitor clomipramine (CMI) intravenously, and, two days later, the PRL responses dopamine receptor blocker haloperidol (HAL), administered intramuscularly. The CMI and HAL tests were also performed in 15 healthy male subjects. The PRL responses to CMI of the patients were blunted compared to healthy controls, while the PRL responses to HAL were not significantly different from controls. Searching for correlations among the maximal PRL responses to the three stimuli in the patient's group, we found that the PRL responses to ECT were significantly correlated to the PRL responses to i. m. HAL (r = 0.8205, N = 15, p < 0.001) and not to the PRL responses to i. v. CMI (r = 0.1713, n. s.). It is suggested that the rises in PRL during ECT reflect the responsivity of the hypothalamus-pituitary dopaminergic system, and seem to be the result of a transient decrease in the inhibitory dopaminergic input of the hypothalamus to the pituitary lactotrophs, caused by the electrical stimulus and the subsequent seizure.